Astronomy Tea Talk

  Observations of the gaseous halos of galaxies (the circumgalactic medium or CGM) are able to constrain important but poorly-understood mechanisms that govern galaxy formation, such as supernovae-driven outflows and gas inflowing along cold-accretion streams. I will present the first results from our group's survey of cool gas in the CGM of Lyman-break selected galaxies at z~2.5, near the peak of the cosmic star formation rate. By comparing the gas absorption features seen towards a background QSO sightline nearby a foreground galaxy to photo-ionization models we measure the metallicity of the gas, which is crucial to determine its origin. Using a new method that includes variations in the shape of the UV radiation illuminating the gas, we derive robust metallicity measurements. We show that metal-enriched gas is found in the CGM up to ~100 kpc from foreground galaxies.